JPH09286758A - Production of highly purified terephthalic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a process flow and to reduce investment and a cost relating to the operation in a production of highly purified terephthalic acid by subjecting an acetic acid solvent slurry of terephthalic acid crystal obtained by a liquid phase oxidation of p-alkylbenzene to a mother liquor substitution and performing a catalytic hydrogenation. SOLUTION: An acetic acid solvent slurry is introduced to an upper part of a mother liquor substituting tower 1 and a sedimentary layer (b) of terephthalic acid crystal is formed on a lower part of the tower by sedimentation of the terephthalic acid crystal, then substituting water in an amount sufficient to form an ascending current of water is supplied from a bottom part to inside the tower, thus the sedimentary layer (b) of the terephthalic acid crystal is taken out from the bottom part of the tower. An arm-type stirring fan 10 is provided in the sedimentary layer (b) and the stirring fan 10 is calmly rotated to keep fluidity of the sedimentary layer (b).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity terephthalic acid, and more particularly to a mother liquor replacement method in which the mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals obtained by a liquid phase oxidation reaction is replaced with water.

[0002]

BACKGROUND OF THE INVENTION Terephthalic acid is produced by a liquid phase oxidation reaction of a p-phenylene compound such as p-alkylbenzene represented by p-xylene. Usually, acetic acid is used as a solvent (mother liquor) for a catalyst such as cobalt and manganese. Use
Alternatively, a catalyst obtained by adding a bromine compound or an accelerator such as acetaldehyde to this is used. However, since this reaction product contains 4-carboxybenzaldehyde (4CBA), paratoluic acid, and various coloring impurities, a highly sophisticated purification technique is required to obtain high-purity terephthalic acid.

As a method for purifying the crude terephthalic acid obtained by the liquid phase oxidation reaction, the crude terephthalic acid is dissolved in a water solvent at high temperature and high pressure and subjected to catalytic hydrogenation treatment, oxidation treatment, recrystallization treatment or terephthalic acid. Various methods such as high temperature immersion treatment in a slurry state in which crystals are partially dissolved are known. In particular, the crude terephthalic acid is dissolved in water and subjected to high temperature and high pressure.
The method of carrying out a catalytic hydrotreating process using a group noble metal catalyst has a history of several decades as a large-scale commercial process for producing high-purity terephthalic acid.

However, in the method of carrying out this catalytic hydrotreating step, one of the major problems is that the process flow is long. In other words, in the process, even if only the main process flows excluding complicated and cumbersome units such as solvent recovery and catalyst recovery are listed, one or two or more stages of oxidation reactor and several crude sequential crystallization It is connected to a vessel, a crude system separator, a crude system dryer, a re-dissolution tank, a catalytic hydrogenation reactor, several purification system sequential crystallizers, a purification system separator, and a purification system dryer.

A major cause of the long process flow is that the reaction solvent for producing crude terephthalic acid by oxidation is acetic acid, and the reaction solvent for purification by catalytic hydrogenation is water. . In order to carry out such solvent replacement of acetic acid with water, the crude terephthalic acid produced by oxidation must be once completely separated from the acetic acid solvent and then redissolved in an aqueous solvent. If the separation of crude terephthalic acid and acetic acid is incomplete and the solvent acetic acid is attached to the crude terephthalic acid and supplied to the catalytic hydrotreating process, acetic acid itself will hardly undergo chemical change by catalytic hydrotreating. Therefore, the solvent acetic acid adhering to the crude terephthalic acid is mixed with the water solvent of the catalytic hydrogenation treatment and discharged out of the system. This means that a valuable substance called acetic acid flows out and is lost, and the acetic acid that flows out must be made harmless to the environment, so that the economical loss becomes large.

In order to suppress this economic loss, acetic acid is added to the crude terephthalic acid sent to the catalytic hydrogenation step by combining a crude system separator for separating the mother liquor from the slurry containing crystals from the oxidation step and a crude dryer. It is necessary to almost completely block the attachment and entrainment, and current commercial scale equipment uses such a combined separator and dryer flow. The most commonly used method for separating the mother liquor from the crystal-containing slurry is a centrifuge or rotary vacuum filter,
Both are widely used for separating the mother liquor from the crude terephthalic acid crystal slurry.

The centrifuge is a method in which a raw material acetic acid slurry is introduced into a basket which is rotating at a high speed, the mother liquor is overflowed from the upper part, and crystals are guided to the lower part. Conservation from constraints,
The disadvantage is that maintenance is complicated. Moreover, since the crude terephthalic acid crystals cannot be easily rinsed, the mother liquor cannot be completely removed. Therefore, it is necessary to provide a drying step downstream of the centrifugation step to remove acetic acid remaining on the crude terephthalic acid crystals. There is.

In the rotary vacuum filter, as the filter medium rotates, the crude terephthalic acid crystals stored at the bottom of the housing adhere to the filter medium and rise and rotate. Generally, after passing through the rinse point, the crystals are separated as a cake. It is a thing. Since high speed rotation is not required in this method,
Although maintenance and maintenance are relatively easy, it is difficult to completely remove the mother liquor adhering to the crude terephthalic acid crystals by rinsing, so that a dryer is required downstream as in the case of the centrifuge.

As a method for separating crystals and removing a mother liquor in place of a centrifuge or a rotary vacuum filter, Japanese Patent Publication No.
For No. 3-5410, a slurry in which crude terephthalic acid was recrystallized with water was passed through a vertical tube at a high temperature (165 ° C or higher), and the terephthalic acid crystals were settled by gravity against the slow upward flow of high temperature water, and adhered. A method of washing the mother liquor is described. In this method, after recrystallizing terephthalic acid crystal in water solvent, the crystal and mother liquor are separated at high temperature (under pressure). Basically, mother liquor replacement method to replace mother liquor of terephthalic acid slurry with fresh solvent Is.

In this mother liquor replacement method, gravity is used for the settling of crystals, and therefore it is excellent in that no special power is required,
It is also attractive that the device itself used is simple. However, it has the drawbacks of low mother liquor substitution rate and difficulty in scaling up experimental results.
In order to improve the mother liquor substitution rate, it is sufficient to increase the upward flow of high temperature water, but for this purpose a large amount of solvent (water) must be used. As a result, a large amount of small-sized crystals overflow from the top of the vertical tube.

In order to overcome such drawbacks, Japanese Patent Laid-Open No. 57-53431 discloses a gravitational sedimentation step and particle transport of terephthalic acid crystals divided by a plurality of lateral partition plates having a large number of holes. We have proposed a mother liquor replacement method that combines processes. Such a partition plate is for preventing channeling or back mixing of the fluid in the apparatus and increasing the mother liquor replacement ratio, but such a partition plate is provided in the mother liquor replacement utilizing gravity sedimentation for handling slurry. That is, the accumulation of crystals on the partition plate, the blockage of the opening and the bulking occur, and a great deal of labor is required to stabilize the operation.

Further, in Japanese Patent Application Laid-Open No. 1-160942, a mother liquor displacement column having a structure in which a large number of laterally partitioned shelves are provided, and terephthalic acid crystals are dropped by scraping blades that rotate relatively slowly on each shelf. In the example in which the acetic acid solvent (mother liquor) of crude terephthalic acid was replaced with water using the displacement column, a high level of mother liquor substitution ratio estimated to be 99% or more was achieved. However, in this example, the amount of terephthalic acid slurry supplied was about 1 ton / h in an apparatus on a laboratory scale, and if this was scaled up to a commercial scale, about 100 times the amount of terephthalic acid slurry as in the example was obtained. If the mother liquor displacement column is to be treated in accordance with the amount to be treated, a cross-sectional area of about 100 times that of the displacement column of the embodiment is required. That is, the rate at which the terephthalic acid crystals settle in the apparatus is determined by the gravity and the characteristics of the solvent. Therefore, the cross-sectional area of the mother liquor substitution tower is about 100 when the conditions are constant regardless of the size of the mother liquor substitution tower.
In order to achieve the above-mentioned high level mother liquor displacement tower, a huge mother liquor displacement tower is required.

[0013]

The mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals obtained by a liquid phase oxidation reaction is replaced with water using a mother liquor displacement column, and the obtained aqueous slurry of crude terephthalic acid is contacted. If introduced to a hydrotreating device, a separator and a dryer for separating the mother liquor from the slurry from the oxidation step in the current process flow can be eliminated. However, as described above, a series of commercial-scale mother liquor substitution methods for producing high-purity terephthalic acid, that is, a practical technology capable of substituting the functions of a crude terephthalic acid mother liquor separator and a dryer in the current process flow, has not been completed yet. I haven't seen it.

The object of the present invention is to replace the mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals obtained by a liquid phase oxidation reaction with water, and subject the obtained mother liquor of an aqueous slurry of crude terephthalic acid to a catalytic hydrogenation treatment as it is. The goal is to complete the method of sending to equipment and shorten the process flow in the high-purity terephthalic acid production plant, which in turn saves investment and reduces operating costs.

Since it is necessary to determine where to set the boundary line between the loss of acetic acid and the economic loss due to the accompanying wastewater treatment load depending on various economic environments in the manufacturing plant, it is difficult to draw a precise line. However, in general, if the mother liquor replacement ratio is 99% or more, it is judged that there is a possibility of implementation on a commercial scale. The mother liquor substitution rate is 99.
If it is possible to achieve a level exceeding 9%, it is judged that the possibility of implementation will become certain. Therefore, a specific object of the present invention is to complete an efficient mother liquor replacement method as compared with the conventional mother liquor replacement method and achieve a mother liquor replacement rate of 99% or more, preferably 99.9% or more.

[0016]

Means for Solving the Problems The inventors of the present invention have conducted many years of research to overcome the technological ideas and progress of the preceding decades, and to overcome those technical obstacles. We found that it is possible to achieve a high mother liquor substitution rate of 99% or more with a small and simple device by forming a terephthalic acid crystal deposition layer at the bottom of the product and supplying water from the bottom of it, and filed a patent application. (Japanese Patent Application No. 7-118299). Furthermore, the inventors of the present invention conducted a study,
By providing a stirring shaft (arm type stirring blade) with a plurality of horizontally extending arms in the deposited layer of terephthalic acid crystals and gently rotating the stirring shaft, the fine fluidity of the deposited layer is maintained, and By imparting pulsation to the terephthalic acid sediment layer in some way, the drift and channeling of the substitution water in the sediment layer is suppressed and the dispersion of the substitution water is improved, and the operability of the mother liquor substitution tower is dramatically improved. The present invention has been achieved and has reached the present invention.

That is, the present invention provides a method for producing high-purity terephthalic acid, which comprises subjecting an acetic acid solvent slurry of terephthalic acid crystals obtained by liquid-phase oxidation of p-alkylbenzene to an aqueous solvent slurry, followed by catalytic hydrogenation treatment. Introducing the acetic acid solvent slurry into the upper part of the mother liquor displacement tower, forming a deposition layer of terephthalic acid crystals in the lower part of the tower by the precipitation of terephthalic acid crystals, and adding sufficient replacement water from the bottom to form an upward flow of water inside the tower. It is supplied, the deposited layer of terephthalic acid crystals is extracted from the bottom of the tower, and an arm type stirring blade is provided in the deposited layer.
A method for producing high-purity terephthalic acid, characterized in that the fluidity of a deposited layer is maintained by gently rotating the stirring blade.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An acetic acid solvent slurry of crude terephthalic acid crystals to be subjected to mother liquor replacement is produced by oxidizing a p-phenylene compound such as p-alkylbenzene, typically paraxylene, and is usually cobalt, manganese or the like. The heavy metal salt catalyst described above, or a catalyst in which a bromine compound or a promoter such as acetaldehyde is added thereto is used. Acetic acid containing about 3 to 20% of water is used as the solvent. Air or oxygen is usually used as molecular oxygen, and the reaction is generally carried out at a temperature of 170 to 230 ° C. and a pressure of 10 to 30 atm in one or more stages.

In addition to terephthalic acid crystals, 4CBA, paratoluic acid, catalysts and various other impurities are contained in the slurry-like reaction effluent after the liquid phase oxidation step. The reaction effluent is introduced into a crude system sequential crystallizer having one or more stages, and while the temperature is successively lowered, the terephthalic acid dissolved in the solvent is further crystallized, and the temperature is lowered to a predetermined temperature. After that, the acetic acid solvent slurry of terephthalic acid crystals is supplied to the mother liquor substitution tower and guided into the rising flow of water in the tower, and the oxidation reaction mother liquor moves upward with the rising liquid flow of water together with a small amount of fine terephthalic acid crystals. Most of the terephthalic acid crystals settle in the tower.

The precipitated terephthalic acid crystals are withdrawn from the bottom of the tower as a slurry, but in the present invention, a sediment layer is formed at the bottom of the tower, and substitution water is supplied from the inside of the sediment layer. In order to improve the dispersion of the replacement water and prevent the channeling and uneven flow of the replacement water, the replacement water is supplied from the arm type stirring blade provided in the deposition layer as if it were a sprinkler or the deposition layer. It is effective to adopt a method of supplying via a ring header provided inside. The sedimentary layer at the bottom of the tower is extracted by a known engineering method by a continuous or intermittent method. As a result, individual terephthalic acid crystals in the deposited layer move downward. On the other hand, since there is an upward flow of water in the tower, the terephthalic acid crystals and water come into countercurrent contact, and the acetic acid solvent adhering to the crystal surface and various oxidation reaction by-product impurities contained in the acetic acid solvent. Etc. will be efficiently cleaned. As a result, an aqueous solvent slurry of terephthalic acid crystals containing almost no acetic acid solvent is extracted from the bottom of the column, and this slurry is subjected to various known purification methods generally without any additional treatment, generally The aqueous solvent slurry can be melted at high temperature and high pressure, and sent to a process for producing high-purity terephthalic acid through a catalytic hydrotreating process using a Group VIII noble metal catalyst.

The main conditions for carrying out the present invention will be described below. The mother liquor replacement ratio in the mother liquor replacement tower is 99.
%, Preferably 99.9% or more is required, and the main condition therefor is to maintain the fluidity of the terephthalic acid crystal deposition layer. Further, it is necessary to properly take the length (height) of the terephthalic acid crystal deposition layer and the linear velocity of water rising in the tower (upper linear velocity).

The length of the deposited layer is determined as a result of a number of operating factors such as the feed rate of the terephthalic acid slurry from the top of the tower, the feed rate of water from the bottom of the tower, and the withdrawal rate of the terephthalic acid slurry from the bottom of the tower. However, in actual operation, it was achieved by detecting the interface between the sedimentation layer and the crystal precipitation part in the mother liquor displacement tower and adjusting the extraction rate of the terephthalic acid crystal deposition layer to keep it at a predetermined position. It If the deposition layer becomes longer, the cleaning effect increases and the mother liquor replacement rate increases, and conversely, if it becomes shorter, the mother liquor replacement rate decreases, so the length of the deposition layer is preferably as long as possible.
If it is too long, blocking may occur due to the static pressure of the terephthalic acid crystal itself, so an unnecessary length should be avoided.

The mother liquor substitution rate is also shown as a function of the column diameter, and in order to achieve a mother liquor substitution rate of 99% or more, it is necessary to make the length of the deposition layer at least one fifth of the diameter of the mother liquor substitution column. is there. The ascending linear velocity represents the flow rate of water countercurrently rising with respect to the terephthalic acid crystals in the sedimentary layer, and is conveniently defined by the superficial standard of the sedimentary layer portion. According to our experience, the mother liquor displacement rate increases with increasing linear velocity, but it is about 3 m.
If it exceeds / h, the mother liquor replacement rate will rapidly decrease.

In the design of the mother liquor displacement column, the lower limit of the rising linear velocity is a value exceeding 0, that is, a substantially rising flow is formed, and the upper limit is about 3 m / h. Setting the rising linear velocity to a value larger than this upper limit not only causes a decrease in the substitution rate, but also some terephthalic acid crystals do not fully settle and are taken out upward together with the rising liquid flow. The increase in the amount used also causes an increase in the concentration of water in the acetic acid mother liquor recovered from the top of the column.

The temperature of the mother liquor displacement tower is not particularly limited,
It is necessary to consider several factors related to the entire high-purity terephthalic acid production equipment. One of them is that performing the mother liquor substitution at a higher temperature has the effect of improving the quality of the obtained terephthalic acid. That is, in a general terephthalic acid production apparatus, most of the terephthalic acid produced by the reaction already exists as crystals at the time of introduction from the oxidation reactor to the crude sequential crystallizer. By successively lowering the temperature in the crystallizer, the remaining portion of terephthalic acid dissolved in the mother liquor is successively crystallized. It is a general phenomenon that the crystals obtained in the high temperature part have higher purity than the crystals obtained in the lower temperature, but in the case of crystallization of terephthalic acid, 4CBA existing as an impurity is terephthalic acid. It is known to co-crystallize with an acid, and the rate of co-crystallizing has the property of rapidly increasing with decreasing temperature. Therefore, if the mother liquor replacement is performed at a higher temperature, the purity of the crude terephthalic acid in the obtained water slurry is improved, and the quality of the high-purity terephthalic acid obtained through the catalytic hydrotreating process is improved.

On the other hand, since the catalytic hydrotreating reaction is carried out at a higher temperature, specifically a temperature exceeding 250 ° C., carrying out the mother liquor replacement at a lower temperature causes a loss of thermal energy. Become. Since the oxidation reaction is carried out at around 200 ° C, if the mother liquor replacement is carried out at a temperature significantly lower than that, energy is lost due to the necessity of repeating the temperature decrease and the temperature rise. Therefore, the mother liquor replacement tower is as close as possible to the oxidation reaction. It is desirable to carry out at temperature.

The mother liquor substitution column in the present invention is an extremely simple device and has few power parts, so that it can be easily carried out at high temperature and high pressure. However, when the temperature is high, the amount of terephthalic acid dissolved in the acetic acid solvent mother liquor flowing out from the top of the mother liquor displacement column is inevitably large. Since this mother liquor is reused as a solvent for the oxidation reaction again, it does not directly lead to the loss of terephthalic acid, but it causes a substantial decrease in the production amount of the reactor. Taking these conditions into consideration, it is preferable that the temperature of the mother liquor replacement step is generally lower than the oxidation reaction temperature within 120 ° C, that is, about 80 to 180 ° C. The pressure of the mother liquor displacement tower is a pressure for maintaining the temperature of acetic acid or water, and when the temperature is determined, the lower limit pressure is automatically determined.
It is about g / cm ² G.

It is important to maintain the fluidity of the terephthalic acid crystal deposition layer in the mother liquor substitution tower. This is because the characteristics of the slurry are lost when the sedimentary layer formed by the precipitation of terephthalic acid crystals becomes completely compacted and cannot be extracted from the mother liquor substitution column by an engineering method. In order to prevent this, it is necessary to constantly flow the deposited layer of terephthalic acid crystals. Further, by maintaining the fluidity of the deposited layer, the dispersion of the supplied substitutional water can be promoted, and the substitutional water can be prevented from drifting upward in the sedimented layer of terephthalic acid crystals and rising or channeling. Of course, when the fluidity of the deposited layer becomes severe, the mass transfer in the deposited layer is promoted, so that the purification capability of the mother liquor displacement column, that is, the mother liquor substitution rate is reduced. In order not to lower the mother liquor substitution ratio more than necessary, it is essential to suppress the fluidity of the deposited layer to a minute level.

The arm-type stirring blade is the most effective method for imparting a minute fluidity to the deposited layer. It is also effective to give pulsation to the deposited layer by some method. The arm type stirring blade may be any one as long as the arm extends in the horizontal direction from the stirring axis, and when viewed from above the stirring axis, there are no particular restrictions on the number or shape of the arms such as one-letter, cross-shaped, and tomo-shaped arms. The number of steps of the arm is determined by the height of the deposited layer, and the cross section of the arm is not particularly limited, such as a circle, a triangle, or a rhombus, as long as it does not require significant power to shear the deposited layer. The rotation speed of the arm type stirring blade is preferably 0.1 to 20 rotations per minute, more preferably 0.5 rotations per minute.
It is 10 revolutions. Regarding the blade diameter of the arm type stirring blade, a length is required to fluidize the entire deposition layer of terephthalic acid crystals. In an actual device, the mother liquor substitution tower has a diameter of 0.7 to
The blade diameter is preferably 0.99 times, and more preferably 0.8 to 0.99 times the diameter of the mother liquor substitution tower.

As a method of giving pulsation to the sedimentary layer, a method of intermittently repeating the supply replacement water at the time of supplying and stopping, a method of adding a pulser to the supply replacement water line to give a pulsation,
There is a method in which a pulsar is directly installed at the bottom of the mother liquor substitution tower, that is, a portion where terephthalic acid crystals are deposited to give pulsation. By providing such an arm-type stirring blade and gently rotating it, the microfluidity of the deposited layer is maintained, and by pulsating the deposited layer of terephthalic acid in some way, The nonuniform flow and channeling of the replacement water are suppressed, the dispersion of the replacement water is improved, and the operability of the mother liquor replacement column is dramatically improved.

[0031]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1 Using the apparatus shown in FIG. 1, an experiment was carried out in which the mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals, which was a raw material slurry obtained by a liquid phase oxidation reaction, was replaced with water. In FIG. 1, the mother liquor substitution tower 1 is a SUS container. A raw material slurry introducing pipe 3 is provided above the mother liquor substitution tower, and is connected to a raw material slurry supply pump 2. There is a mother liquor discharge pipe 4 at the top of the tower. The bottom of the mother liquor substitution tower has a semi-elliptical dish structure and is connected to the slurry tank 9. The slurry tank 9 is circulated and stirred by a circulation pump 12 installed outside. A branch pipe to the slurry extraction pump 13 and a branch pipe to the water supply pump 14 are connected in the middle of the return pipe from the circulation pump 12.

A screw conveyor guide tube 6 is inserted and connected to the bottom of the tower, and is obliquely cut upward to form a deposited layer extraction port 7. A screw conveyor 5 is contained inside the screw guide tube 6, one end of which reaches the crystal extracting port 7, and the other end of which reaches the upper portion of the slurry tank 9. The screw conveyor 5 is connected to a motor 8 installed outside. A horizontal line a at the center of the mother liquor displacement tower 1 is the upper surface of the terephthalic acid crystal deposition layer, and the screw line 6 is provided from the horizontal line a.
The length (height) of the deposited layer is the length to the upper end of.

In FIG. 1, first, the water supply pump 14 was driven to inject 100 ° C. water into the system. After water began to overflow from the mother liquor discharge pipe 4, the circulation pump 12 and the slurry extraction pump 13 were operated. Further, the motor 11 was operated to rotate the arm type stirring blade 10 at a speed of 4 rotations per minute. Next, the raw material slurry supply pump 2 was operated to supply the raw material slurry at 150 ° C. through the raw material slurry introducing pipe 3. The raw material slurry used was an acetic acid solvent slurry of terephthalic acid produced on a commercial scale. The raw material slurry uses para-xylene as an oxidation reaction catalyst and cobalt, manganese, and bromine compounds, and the reaction temperature is 1
It is a reaction product obtained by oxidizing air by blowing air into a water-containing acetic acid solvent at 95 ° C. The reaction product was made into a slurry cooled to 150 ° C. via several stages of sequentially lowered crystallizers, and this slurry was supplied to the mother liquor substitution column 1. When the height of the deposited layer reached a predetermined position while being detected by the powder surface detector, the motor 8 was operated to rotate the crystal extracting screw conveyor 5 to start the crystal extracting.

After the system became a steady state, each flow rate was adjusted and set as follows. Raw material slurry supply pump 2 783 kg / h (crystal concentration 32.4%) Slurry extraction pump 13 762 kg / h (crystal concentration 33.3%) Water supply pump 14 586 kg / h The height of the deposited layer is at a predetermined position. The rotation speed of the motor 8 was adjusted while monitoring with a powder surface detector so that it might be maintained.
The rising linear velocity of water in the tower under this condition is 0.
It will be 88 m / h.

At the point of time when continuous operation was carried out for 3 days, samples were taken at each point of the apparatus, and the results of analyzing each composition were as follows. Mother liquor of raw material slurry (supernatant liquid obtained by cooling sample taken from raw material slurry supply pump 2 to room temperature and leaving still) Acetic acid 85.2% Water 14.5% Unknown 0.3% Slurry (slurry extraction pump 13 The sample collected from the above was cooled to room temperature and left to stand.) Acetic acid 0.102% From this, the mother liquor substitution rate based on acetic acid was calculated to be 99.9%.
Becomes

Comparative Example 1 In Example 1, when the operation was carried out with the rotation of the arm type stirring blades stopped, the fluidity of the sediment layer was lost, channeling of the upward flow of the replacement water occurred, and further bulking at the bottom of the column. Occurred and the extraction of crystals from the bottom of the column became unstable, and the operation could not be performed.

[0038]

In the method for producing high-purity terephthalic acid according to the present invention, an extremely high mother liquor substitution rate is obtained and the arm type stirring blade provided in the deposited layer is gently rotated to maintain the fluidity of the deposited layer. As a result, the operability of the mother liquor replacement device is significantly improved. This mother liquor replacement method eliminates the need for a mother liquor separator and dryer for crude terephthalic acid obtained by liquid phase oxidation reaction. Also, this mother liquor displacement column is a small and simple device, and it is easy to scale up from a laboratory scale device to a commercial scale device. Further, since the mother liquor substitution column can be easily operated at high temperature and high pressure, it is possible to obtain higher quality and high purity terephthalic acid and to reduce the number of crude terephthalic acid crystallizers.

Therefore, the process flow, which is one of the major problems in the conventional high-purity terephthalic acid production method, is shortened, the construction cost in the high-purity terephthalic acid production is significantly reduced, and the operation is easy. Become. Further, in the high-purity terephthalic acid production method of the present invention, the utility cost consumed by the mother liquor separator and dryer of crude terephthalic acid will be reduced, and an extremely high mother liquor substitution rate can be obtained. The outflow of acetic acid, which is the solvent for the liquid-phase oxidation reaction, was reduced, and the load on wastewater treatment hardly increased. Therefore, according to the present invention, the production of highly purified terephthalic acid, which is extremely advantageous commercially, can be carried out.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a mother liquor replacement device used in Examples.

[Explanation of symbols]

 1: Mother liquor replacement tower 2: Raw material slurry supply pump 3: Raw material slurry introduction pipe 4: Mother liquor discharge pipe 5: Crystal extraction screw conveyor 6: Screw conveyor guide pipe 7: Crystal extraction port 8: Motor 9: Slurry tank 10: Arm Stirrer 11: Motor 12: Circulation pump 13: Slurry extraction pump 14: Water supply pump a (Rental line): Upper surface of deposited layer b: Deposited layer of terephthalic acid crystals

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Fumio Ogoshi 3-10 Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture Mitsubishi Gas Chemical Co., Ltd. Mizushima Plant (72) Inventor Masato Inari 3-10 Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture Address: Mitsubishi Gas Chemical Co., Ltd., Mizushima Plant

Claims (6)

[Claims] 1. A method for producing high-purity terephthalic acid, which comprises subjecting an acetic acid solvent slurry of terephthalic acid crystals obtained by liquid-phase oxidation of p-alkylbenzene to an aqueous solvent slurry, and then performing catalytic hydrogenation treatment to replace the mother liquor. Introducing the acetic acid solvent slurry in the upper part of the tower, to form a deposited layer of terephthalic acid crystals in the lower part of the tower by sedimentation of terephthalic acid crystals,
Supplying sufficient displacement water to form an upward flow of water from the bottom to the inside of the tower, extracting the terephthalic acid crystal deposition layer from the bottom of the tower, installing an arm type stirring blade in the deposition layer, and gently rotating the stirring blade. A method for producing high-purity terephthalic acid, characterized in that the fluidity of the deposited layer is maintained by allowing it to 2. The method for producing high-purity terephthalic acid according to claim 1, wherein the replacement water is intermittently supplied. 3. The method for producing high-purity terephthalic acid according to claim 1, wherein the replacement water is supplied while being pulsed. 4. The method for producing high-purity terephthalic acid according to claim 1, wherein a pulse is applied to the bottom of the mother liquor displacement column. 5. The rotation speed of the arm type stirring blade is 0.1 to 2 per minute.
The method for producing high-purity terephthalic acid according to claim 1, wherein the number of revolutions is 0. 6. The method for producing high-purity terephthalic acid according to claim 1, wherein the displacement water from the bottom of the deposited layer is supplied from a stirring blade provided in the deposited layer.